A British publicist has claimed to be the go-between for Donald Trump Jr and a Russian lawyer, amid mounting concern over possible collusion between the Trump campaign and Moscow.

Mr Trump Jr, the eldest son of the president, met Natalia Veselnitskaya, who said she had damaging material about Hillary Clinton, on June 9 2016 at Trump Tower.

Rob Goldstone

The encounter was set up by Rob Goldstone, a New York-based former journalist, whose PR firm describes the Manchester-born executive as having represented Michael Jackson, BB King and Sir Richard Branson.

Mr Trump Jr said that the meeting did not provide any information about Mrs Clinton, and that he was lured there under false pretences.

Ms Veselnitskaya, who is married to a Moscow government official, has denied that she works for the Kremlin.

"I was asked by my client in Moscow - Emin Agalarov - to help facilitate a meeting between a Russian attorney (Natalia Veselnitzkaya) and Donald Trump Jr,” said Mr Goldstone, in a statement provided to The Telegraph.

“The lawyer had apparently stated she had some information regarding illegal campaign contributions to the DNC which she believed Mr Trump Jr. might find important. I reached out to Donald Trump Jr. and he agreed to squeeze us into a very tight meeting schedule.

“At the meeting, the Russian attorney presented a few very general remarks regarding campaign funding and then quickly turned the topic to that of the Magnitsky Act and the banned US adoption of Russian children - at which point the meeting was halted by Don Jr. and we left. Nothing came of that meeting and there was no follow up between the parties."

His client, Emin Agalarov, a Russian pop singer, is the son of Aras Agalarov, a billionaire tycoon who sponsored the 2013 Miss Universe pageant, which was owned by Donald Trump.

Mr Trump Jr issued two statements about the meeting, when approached by The New York Times. First, he said it was an encounter to discuss adoption. Then he admitted that he hoped the Russian lawyer would provide damaging material on his father’s rival.

“Obviously I’m the first person on a campaign to ever take a meeting or hear info about an opponent,” he tweeted on Monday. “Went nowhere but had to listen.”

Emin Agalarov in a still from his music video - in which Donald Trump makes a cameo

Mr Trump Jr. has hired a lawyer to represent him in Russia-related investigations, his office and the lawyer said on Monday.

His lawyer Alan Futerfas, who specialises in criminal defence, would not say when he was retained or whether he played any part in the statements Trump Jr. made over the weekend about a meeting with a Russian lawyer.

A Republican member of the US Senate Intelligence Committee, Susan Collins, called on Mr Trump Jr. to testify before the panel, which is looking into accusations of Russian meddling in the election.

Trump Jr: I would have done things differently

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"Our intelligence committee needs to interview him and others who attended the meeting," Senator Susan Collins told reporters at the US Capitol.

Senator Mark Warner, the top Democrat on the Senate Intelligence Committee, said the panel "absolutely" wants to speak to Mr Trump Jr. about the meeting. Mr Warner said he and the Republican committee chairman, Richard Burr, will decide later whether to ask Trump Jr. to testify in public or in a classified setting.

He also wants to speak to anyone else involved, which would include Mr Goldstone and his pop star client Emin Agalarov. The committee is investigating whether there was any collusion between the Trump campaign and Russia.

Mr Warner said: "This is the first time that the public has seen clear evidence of senior level members of the Trump campaign meeting with Russians."

Mr Trump Jr tweeted: "Happy to work with the committee to pass on what I know."

The president was also on Monday trying to deflect criticism of his daughter, Ivanka, after she sat in his chair during a meeting at the G20 attended by Xi Jinping, the Chinese president, Angela Merkel, the German chancellor and Russia's Vladimir Putin.

Ivanka Trump at the G20 with her father and the leaders of Japan, Germany and Canada, plus World Bank president Jim Yong Kim

Mr Trump described having his daughter take his place as “standard.”

“If Chelsea Clinton were asked to hold the seat for her mother, as her mother gave our country away, the Fake News would say CHELSEA FOR PRES,” [sic] he tweeted.

“It would never have occurred to my mother or father to ask me,” Ms Clinton replied. “Were you giving our country away? Hoping not.”

Lindsey Graham, a member of the Senate's armed services committee, said the idea of a joint cyber security unit was "not the dumbest idea I've ever heard, but it's pretty close."

Mr Trump said: "The fact that President Putin and I discussed a Cyber Security unit doesn't mean I think it can happen."

Mr Trump said the two countries could work together on some areas, including on Syria, where he said a ceasefire that began on Sunday would "save lives."

He also spent the day goading the Republican-led US Congress to pass major healthcare legislation, saying they would not “dare” leave for the summer recess in August “without a beautiful new health care bill fully approved and ready to go!”